I've got the whole "kit" for my M249S - para barrel, regular barrel - both old and new style, all the available stock options (para, savit, regular clubfoot, new style hydraulic and even the minimi), both bipods, etc... so it made sense for me to get the M145, but I'm not convinced that it's a great option for this semi-auto belt fed. Full auto, sure - but semi-auto... ?
I wonder how accurate the M249S is. The quick-change barrel system is the antithesis of accuracy - and it's not a concern when you have a full auto squad support weapon. In fact, IIRC, the M249 is a 12 MOA weapon.
Has anyone actually shot the M249S for groups at 100 yards?